JPH01214346A - Ultrasonic transmitting circuit - Google Patents

Abstract

PURPOSE:To prevent a change in a propagation delay time and to realize the convergence of beam reduced in a side lobe as desired, by connecting a constant voltage source to the base of a bipolar transistor, wherein the drain of MOSFET is connected to an emitter and drive voltage is supplied to a collector through a resistor, through a resistor. CONSTITUTION:In order to make the voltage Vds between a drain and a source constant regardless of the magnitude of drive voltage Vdd, a bipolar transistor Q4 is connected between MOSFET Q3 and a resistor R2. The drain of MOSFET Q3 is connected to the emitter of the bipolar transistor Q4 and, when the collector Q4 and the base thereof are connected to an amplifying stage Vc through resistors R2, R3, emitter potential is determined by base potential and almost equal to Vc and the voltage between the drain and source of Q3 becomes constant. Even when the drive voltage given to each driver is made different corresponding to a weighting value when the weighting of the transmission intensity at every element is performed in order to reduce a side lobe, propagation delay becomes the same value in all of drivers and delay difference exerting effect on the convergence of beam and fan-shaped scanning is not generated.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields (Figures 4 and 5) Prior Art (Figure 6) Means for Solving the Problems to be Solved by the Invention (Part 1 Figure) Working Example (a) Explanation of one embodiment (Figs. 2 and 3) (b) Explanation of other embodiments Effects of the invention [Summary] An array type transducer is driven by a driver to generate ultrasonic waves. In ultrasonic transmitter circuits for transmitting ultrasonic waves with small side lobes, beam focusing that prevents propagation delay time from changing due to changes in drive voltage and reduces side lobes. For the purpose of realizing the above as desired, an array type transducer consisting of a plurality of ultrasonic transducers arranged, a driver for driving each ultrasonic transducer, and an ultrasonic transducer attached to the driver are provided. In an ultrasonic transmission circuit having a drive timing signal of
MO whose source is grounded and operates according to the drive timing signal
SFET, and a bipolar transistor in which the drain of the MO3FET is connected to the emitter and the drive voltage is supplied to the collector via a resistor, and a constant voltage source is connected to the base of the bipolar transistor via the resistor. Connected.

[Industrial application field]

The present invention relates to an ultrasonic transmitting circuit for transmitting ultrasonic waves with small side lobes in an ultrasonic transmitting apparatus that drives an array type transducer with a driver and transmits ultrasonic waves.

Measurement using ultrasonic waves is widely used in ultrasonic diagnostic devices and the like, and therefore an ultrasonic transmitting circuit is used.

For example, in the ultrasound diagnostic apparatus shown in FIG. 4, a large number of ultrasound transducers (ultrasonic transmitting and receiving elements) 11 to
Array type probe (transducer) 1 with 1N arranged
is used.

Each element 11 to 1N of the array type probe 1 is connected to a driver D1.
~DN to the transmitting circuit system 2, and through preamplifiers R1 to RN to the receiving circuit system 3.

Each transmission circuit system 2 and reception circuit system 3 are connected to a control circuit system 4 and are synchronously controlled, and a display device 5 is connected to the reception circuit system 3.

In such an ultrasonic diagnostic apparatus, each element 11 to 1N
If an appropriate delay element is inserted into the drive circuit of
) and (C), the beam direction can be made radial, and fan-shaped scanning can be performed. It is also possible to focus the beam.

In other words, as shown in Fig. 5 (A), among the elements that are driven simultaneously with a delay circuit interposed, those near both ends are driven early, and those near the center are driven late, so that the ultrasonic waves emitted from each element are The wavefront of the beam becomes W, and the combined beam is focused.

In response to such transmitted ultrasound, the ultrasound reflected from the subject enters the elements 11 to 1N again and is converted into an electrical signal, passes through preamplifiers R1 to RN, is added and amplified by the receiving circuit system 3, and is sent to the display device 5. will be displayed.

In this way, the tomographic image and blood flow information of the subject are displayed on the display device 5 and can be used for diagnosis of the subject.

When we take the intensity distribution of such a combined beam of transmitted ultrasonic waves, as shown in Fig. 5(A), in addition to the main rope MR appearing in the wavefront traveling direction, there are side lobes SR that extend diagonally to the left and right. appears.

This side lobe SR is generated in an unnecessary direction because the actual aperture has a finite length.

Since the existence of this side lobe SR is undesirable, it is desired that it be small (weak). As shown in FIG. 5(B), side lobes can be reduced by gradually increasing the drive voltage Vdd of the elements 11 to 1N from both ends toward the center to make the intensity distribution a Gaussian distribution.

In this way, each element 1
Although the transmitter circuit drives 1 to 1N with different drive voltages, it is hoped that this will not degrade the drive characteristics.

[Conventional technology]

FIG. 6 is an explanatory diagram of the prior art.

As shown in FIG. 6(A), the driver 6 consists of transristors Q, -Q, resistors R1, R2, diodes d, and capacitor CI, and the ultrasonic transmitting/receiving element 11 is connected via coupling capacitor CI and resistor R2. It is driven by the output voltage Vdd mentioned above.

Although not shown, ultrasonic transmitting and receiving elements 12.13, -11N
The same applies to the driver 6, preamplifier R, etc., which are provided for each element.

Here, the transistors Q, , Q, etc. constitute an amplifier.

When not transmitting, the timing signal DT is on, turning on transistor Q, so transistor Q2 is off, transistor Q3 is also off, and element 11 is turned on.
receives the drive output voltage Vdd through a resistor R2 and a coupling capacitor C1.

For transmission, when the timing signal DT turns off, transistor Q1 turns off, transistor Q2 turns on,
Transistor Q3 is also turned on, and the accumulated voltage is discharged in the circuit of element 11, coupling capacitor C1, and transistor Q3, which causes element 11 to generate ultrasonic vibrations.

This is done by lowering the element drive voltage Vdd to reduce sidelobes.

[Problem to be solved by the invention]

By the way, the output transistor Q3 of the driver 6 is MO
This MOSFET has a small on-resistance and realizes efficient transmission operation of the element 11.

However, MOS FET Q 3 does not turn on immediately when the gate signal is applied, but there is some propagation delay. Moreover, this delay changes depending on the drain-source voltage, so if the drive voltage is lowered to reduce sidelobes, the delay time τ will also change as shown in Figure 6 (B), and the delay time τ will change due to beam focusing or fan scanning. There is a problem in that the delay time added to the beam deviates from a desired value, which may impede beam focusing or scanning.

For example, if the ultrasonic transmission frequency f is 3.5 M)Iz, the period is 286 ns, but a time difference of about 1/16 period, that is, 18 na or more affects beam focusing and fan scanning, but the driving voltage Vdd When changing 40V, 25n
There was a delay time difference of 3.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic transmitting circuit that can prevent changes in propagation delay time due to changes in drive voltage and can achieve desired beam focusing with reduced side lobes.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the present invention.

In the figure, the same components as those shown in FIGS. 4 and 6 are indicated by the same symbols. Q4 is a bipolar transistor, and the emitter of Q4 is connected to the drain of MO3FETQ3. A drive voltage Vdd is applied to the collector via a resistor R2.

In the present invention, the emitter of a bipolar transistor Q4 is connected to the drain of the MO3FETQ of the driver 6.

Moreover, the present invention further connects the gate of MO3FET Q3 and the base of Q4 with a capacitor C2.

[Effect]

The delay time of the MO3FETQ changes depending on the change in the drain-source voltage Vds.

Therefore, in the present invention, in order to keep the drain-source voltage Vds constant regardless of the magnitude of the drive voltage Vdd,
A bipolar transistor Q4 is connected between the drain of MO3FETQ and R2.

The drain of MO3FETQ3 is connected to the emitter of bipolar transistor Q4, and the collector of Q4 is connected to Rt, Q
If the base of a is connected to Vc via R3, the emitter potential is determined by the base potential and is approximately equal to Vc.

Therefore, the drain-source voltage of Q3 remains constant regardless of the magnitude of the drive voltage.

Therefore, when weighting the transmission strength of each element for sidelobe reduction, the propagation delay remains the same for all drivers, even though the weighting of the drive voltage applied to each driver differs depending on the value. Therefore, there are no delay differences that affect beam focusing, fan scanning, etc.

Further, by providing the capacitor C2, a differential circuit of the resistor R3 and the capacitor C2 is formed, and the bipolar transistor Q4 is operated at high speed, thereby preventing negative layer propagation delay.

〔Example〕

(a) Description of one embodiment FIG. 2 is a configuration diagram of an embodiment of the present invention.

In the figure, the same components as those shown in FIGS. 1 and 6 are indicated by the same symbols, and R1 is a resistor that connects the power supply Vc and the base of the bipolar transistor Q4;
C2 is a coupling capacitor, which connects the base of bipolar transistor Q4 and the gate of MO3FETQ.

21 is a transmission control circuit which generates a timing signal TD delayed according to the delay amount dβ from the control circuit system 4 in FIG. 22 is a storage device, each weighting stores a driving voltage value corresponding to the value Wa, and the weighting of the transmission control circuit 21 outputs a driving voltage value corresponding to the value Wa. .

23 is a D/A (digital/analog) converter;
An amplifier 24 converts the drive voltage value of the storage device 22 into an analog quantity, which amplifies the output of the D/A converter 23 and supplies the drive voltage Vdd to the driver 6.

FIG. 3 is a characteristic diagram of the MOSFET.

To drive the MOS FET Qs, it is necessary to charge and discharge the gate input capacitance.

In FIG. 3A, dynamic characteristics are shown with the horizontal axis representing the gate charge QG (picocoulombs) and the vertical axis representing the gate-source voltage VCS (volts).

This VGS characteristic has three regions A1, A2, and A3, and region A1 is a region where VCS is between zero and dark value voltage (■), and transistor Q3 is off. It can be seen that the gate capacitance remains constant during this period.

It can be seen that in region A2, the rate of increase in VCS is rapidly decreasing, and therefore the gate capacitance is significantly increasing. In this region A2, the drain-source 1m voltage VOS
decreases rapidly and transistor Q3 begins to turn on), and a Miller capacitance appears on the input side.

In region A3, the slope of VCS becomes large again;
Unlike 1, it is quite linear. In this region, the transistor Q3 is in the on state, and (2). , does not change,
No mirror effect appears.

Figure 3 (B ).

In the figure, curve a3, ax % al is VD! The characteristics are when the power supply voltage Vdd is 60V, 40V, and 20V. The curves b0, bl, b2, and b3 have three characteristics, and are the characteristics when Vdd is OV, 20V, 40V, and 6°.

From this characteristic diagram, it can be seen that the higher Vdd is, the wider the area A2 is.

That is, as the drive voltage Vdd becomes higher, the amount of charge that must be charged to the gate increases, and the timing at which the MOSFET is turned on is delayed.

For example, when comparing the drive voltage of 60V and 20V,
Looking at FIG. 3(B), the difference between the gate storage charge Q at 60V and 20V is about 2500 picocoulombs. Amplify the signal from the control circuit 21, MOSFET
The output current of the small transistors Q+ and Qz that drive Q3 is about 1ooIIIA at most, so the difference is 2500X10-''/1ooox 10-3=25X
10-'=25ns.

The frequency f of the ultrasonic waves generated by the ultrasonic transmitting/receiving element is 3.5.
Assuming M1(z, the period is 286 ns. According to calculations, a time difference of 1/16 period, 18 ns or more affects beam focusing, fan scanning, etc.).

Therefore, as in the embodiment shown in FIG. 2, a bipolar transistor Q4 is connected between the drain of MO3FET Q3 and R2. The potential of the drain of Q3, that is, the emitter of Q4 is Q4
is determined by the base potential of , and is approximately equal to Vc.

Therefore, when MOS FET Q3 is off, bipolar transistor Q is also off, and the base potential of bipolar transistor Q4 is equal to Vc, and the emitter of Q4 and the drain potential of Q3 are also approximately equal to Vc. .

Therefore, the drain-source voltage of MOS FET Q3 does not depend on Vdd, that is, the drive voltage. Also, when a signal that turns on MOS FET Qs is applied to the gate, the differential current of that signal is applied to the bipolar transistor Q by capacitor C3 and resistor R3.
Since it is applied to the base of MO3FE T Q s
and bipolar transistor Q4 are turned on at the same time, and a driving pulse is sent to the ultrasonic transmitting/receiving element as in the conventional case.

The drive voltage value is stored in the storage device 22, and is read out, subjected to D/A conversion by the converter 23, and input to the amplifier 24 to obtain the required drive voltage.

The drive timing for beam focusing, fan scanning, etc. is delayed by adjusting the timing at which the control circuit 21 turns on the transistor Q.

(b) Description of other embodiments In the above embodiments, an example in which the ultrasonic transmitting circuit is used in an ultrasonic diagnostic apparatus has been described, but it may also be used in other ultrasonic equipment, and the transmission control unit 2 may also be used in other embodiments. It may have the following configuration.

Further, the amplification stage of the driver 6 may have another configuration.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, even if the element drive voltage is changed to reduce sidelobes, the propagation delay time can be prevented from changing, and the element drive timing can be prevented from shifting. Focusing and scanning can be performed on schedule.

Further, since the MOS FET only needs to have a low breakdown voltage, it is not necessary to use an expensive MOS FET with a high breakdown voltage, and the structure and control are also simple.

Furthermore, the voltage change on the drain side of the MOSFET is smaller than in the past, making it possible to prevent an increase in feedback capacitance due to the Miller effect.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a configuration diagram of an embodiment of the present invention, Fig. 3 is a characteristic diagram of MOSFET, Fig. 4 is an explanatory diagram of an ultrasonic diagnostic device, and Fig. 5 is a side lobe. Figure 6 is an explanatory diagram of the prior art. In the figure, 1- array type probe (transducer), 2-
Transmission control unit, 6-driver, 11-1N-ultrasonic transducer, Q, -, M
O.S.F.E.T. Q4...-Bipolar transistor.

Claims (2)

[Claims] (1) An array type transducer (1) formed by arranging a plurality of ultrasonic transducers (11 to 1N), a driver (6) that drives each ultrasonic transducer (11 to 1N), and the driver (6). Ultrasonic transducer (11-1
In an ultrasonic transmission circuit having a drive timing signal (N) and a transmission control unit (2) that provides a drive voltage for sidelobe reduction, the driver (6) is source-grounded and operates based on the drive timing signal. MO to do
SFET (Q_3); and a bipolar transistor (Q_4) in which the drain of the MOSFET (Q_3) is connected to the emitter and the drive voltage is supplied to the collector via the resistor (R_2), and the bipolar transistor (Q_4) ) to the base of the resistance (
An ultrasonic transmitting circuit characterized in that a constant voltage source (Vc) is connected via R_3). (2) The ultrasonic transmitting circuit according to claim 1, wherein the base of the bipolar transistor (Q_4) and the gate of the MOSFET (Q_3) are connected by a capacitor (C_2).